Flattening Slabs

Flattening Slabs

Why Good Milling Is About What You Preserve

Flattening a slab sounds simple: put the table in the mill and make it flat. In practice, it is really an exercise in preservation.

For epoxy tables, we generally do not begin milling until all casting is complete. The slab comes into the shop at full thickness, the mold is built, and every epoxy pour is finished before we start reducing material. That is especially important when a design includes multiple colors, clear sections, or layered pours. If you mill between pours, then mill again to correct the next stage, you can slowly destroy the thickness of the table before the build is even complete.

Complete the casting first. Mill the table second.

Flattening Is Really Gauging

Once the epoxy is fully cured, the next step is what we call gauging. The goal is not simply to make the top flat. We are positioning the entire table so that, after both faces are machined, the top and bottom are flat, parallel, and as much of the original thickness as possible has been preserved.

A slab may shift slightly during casting. Epoxy can overflow. One corner may sit higher than another, or the whole piece may carry a small twist. If we simply place it in the mill and start cutting, we may remove far more material than necessary.

We use aluminum set blocks and fine shims to adjust the slab in very small increments, sometimes as little as 1/128 of an inch. We lift and support different points until we find the position that lets us flatten both sides while sacrificing the least material. A tiny adjustment at one corner can preserve an extra eighth or quarter inch across the finished table

Every Pass Costs Something

My mill is manual, so the cutter head moves across the slab by hand. That makes speed important. Move too quickly and the cutter can leave repeating arc marks across the surface - what I call smiley marks. Move too slowly and you can burn the wood.

Burn marks are especially frustrating because the damage is not always only on the surface. Sanding them out can take forever, and sometimes the practical correction is another milling pass. Each correction costs thickness.

A poor setup, an uneven pass, or a burn mark can become a series of small corrections. Before long, an eighth or even a quarter inch is gone.

Thickness Is Part of the Design

That matters because thickness is not just a measurement. It is part of the table's visual presence. Clients choose slab furniture because of its mass, character, and strength. A two-inch slab feels substantial. A three- inch slab can feel almost architectural.

I learned that lesson the hard way once. I started with a slab that was roughly two inches thick and, through a series of corrections, milled it down to about an inch and a quarter. It was devastating. The table had lost the visual weight that made the original slab special. I eventually rebuilt the design and brought the finished table back to about three inches thick, but the lesson stayed with me: you cannot put the original slab back once you have milled it away.

Repair What You Can. Preserve What You Cannot Replace.

Milling can expose tear-out, small voids, or bubbles in the epoxy. Most of those problems can be repaired. Wood tear-out can sometimes be incorporated into the design and filled with epoxy. Small epoxy voids can be infilled with matching material.

Lost thickness is different. Once it is gone, it is gone.

That is why good flattening is really about restraint. The goal is not to keep removing material until the table looks perfect. The goal is to remove only what is necessary to make the table flat, parallel, and ready for the next stage.

Final Thoughts

A finished tabletop may look simple: flat on top, flat on the bottom, and consistent in thickness. Getting there requires careful setup, controlled milling, and constant awareness of what every pass is costing.

Good flattening is almost invisible in the finished table. You do not notice what was taken away. You notice what was preserved.